Our lab has shown that the S100B protein binds to wild-type p53 in primary malignant melanoma, dissociates the p53 tetramer, and down-regulates p53-dependent tumor suppression;therefore, it is important to develop inhibitors of the S100B-p53 interaction to restore wild-type p53 activity in this cancer. As a proof of principle, we have also demonstrated that inhibiting S100B with small interfering antisense RNA (siRNASIOOB) restores wild-type p53 tumor suppressor activity in primary malignant melanoma. Accordingly, we hypothesize that low molecular weight compounds can be rationally designed to bind the well-defined p53 binding site on S100B with high affinity and inhibit the S100B-p53 interaction. This hypothesis will be tested further in the proposed study, via discovery and synthesis of such molecules with the following specific aims. In Aim 1, computer aided drug design (CADD), combined with high- throughput/automated NMR, thermodynamic binding and p53 functional assays will be used to discover lead compounds that bind S100B and inhibit the S100B-p53 interaction. In Aim 2, 3D structures of S100B-drug complexes will be determined using NMR spectroscopy and/or X-ray crystallography. Such structure determinations are already underway. In Aim 3, optimization of lead compounds that inhibit the S100B-p53 interaction will be performed via chemical modifications. Organic syntheses will be guided by 3D structural data (from Aim 2) and CADD lead optimization approaches. Testing of new analogues will be performed using existing thermodynamic binding and biological assays (as in Aim 1). With this strategy, it is our aim to discover/synthesize new compounds that bind S100B and restore p53 activity in malignant melanoma. In the future, the most promising compounds will be examined for efficacy in treating melanoma in animal models. Inhibitors such as these will likely have therapeutic value for treatment of other cancers that have elevated S100B levels and wild-type p53 such as astrocytomas, renal tumors and malignant mature T-cells in leukemia patients.